In general, a multiprojection system includes a screen on which to project an image, a plurality of projectors for projecting images to respective assigned areas on the screen, and a projector array controller for supplying, to each projector, a video signal associated with an image to be projected by each projector.
A seamless projection system is known as one type of multiprojection system. In the seamless projection system, a plurality of images are projected by a plurality of projectors onto a screen such that the images are partially overlapped on the screen, thereby forming a single seamless image. To obtain a single image on a screen in such a seamless projection system, it is necessary to precisely align individual images projected on the screen such that edge lines of adjacent individual images precisely coincide with each other.
In the multiprojection system, respective projectors are different in luminance and color, and thus correction in terms of luminance and color is necessary.
A known method or apparatus for calculating image correction data used to correct luminance difference or color difference may be found, for example, in Japanese Unexamined Patent Application Publication No. 7-226862 (first conventional technique) or Japanese Unexamined Patent Application Publication No. 5-173523 (second conventional technique).
In the first conventional technique, an output signal of an image signal associated with an image to be projected is compared with a reference signal prepared in advance. Image correction data is produced on the basis of a difference detected in the comparison. The image signal is corrected by applying the produced image correction data to the image signal, and the resultant output signal is compared with the reference signal. The above process is performed repeatedly until optimum image correction data, which allows the output signal to be substantially equal to the reference signal, is obtained.
In the second conventional technique, an image signal with a uniform and constant level is input to respective projectors of a multiprojection system, and, first, an adjustment is made such that the output signal level of each projector becomes uniform. Then, a further adjustment is made such that the output signal levels of the respective projectors become equal to each other. Final adjusted values used in the above adjustment are employed as image correction data.
Any projector has more or less nonuniformity of luminance because the input-output characteristic representing the relationship between the level of an input image signal and the corresponding level of output luminance signal varies depending on the display position (hereinafter, the input-output characteristic will be referred to as a gamma characteristic). In the case of a color projector, more or less nonuniformity of color occurs owing to differences in gamma characteristic among primary colors.
In particular, in a multiprojection system, because one screen is formed using a plurality of projectors, differences in gamma characteristic among projectors can cause rather large nonuniformity in luminance and/or color. In a case of a seamless multiprojection system, the gamma characteristic in overlapping areas is influenced by a plurality of projectors.
In the method of producing shading correction data according to the first conventional technique, correction data is produced such that nonuniformity in luminance and color is eliminated at a signal level of an image to be displayed. Therefore, although nonuniformity in luminance and color is corrected for an input image with a particular signal level, nonuniformity in luminance or color is not necessarily eliminated for input images with other different signal levels.
In the second conventional technique, image correction data used to correct luminance nonuniformity in a multiprojection system is produced as follows. First, an adjustment is made for each projector such that luminance nonuniformity is eliminated, and then a further adjustment is made such that luminance differences among projectors are minimized. The adjustment data finally used in the adjustment is employed as the image correction data. In this method, a large number of steps are needed to produce the image correction data. Besides, it is not possible practically to acquire image correction data for each display position. When projectors have overlap areas on a screen as in seamless multiprojection systems, each overlap area is influenced by corresponding two projectors. This makes it very difficult to obtain accurate image-correct data because it is necessary to simultaneously make an adjustment of luminance uniformity and color uniformity within each projector and also among the projectors.
In view of the above, it is an object of the present invention to provide a method and apparatus for calculating image correction data, which allow automatic and easy production of image correction data for each display position of a projector, for use in reducing at least one of luminance nonuniformity and color nonuniformity.
It is another object of the present invention to provide a projection system capable of projecting a seamless image whose luminance nonuniformity and/or color nonuniformity are reduced using produced image correction data, for all input image signal levels.